When you’re new to microscopy or working with agar plates, it can feel impossible to know what’s healthy mycelium and what’s contamination. Even experienced mycologists second-guess themselves sometimes — so don’t worry if you’re unsure.

This guide shows you exactly what to look for, using real-world examples, clear descriptions, and simple rules you can follow every single time.

⭐ What Clean, Healthy Mycelium Looks Like

Healthy mycelium has very distinct features. If what you’re seeing matches these, it’s almost always clean.

✔️ 1. Colour: bright white

All healthy mushroom mycelium is white. Never grey, green, black, pink, or yellow.

✔️ 2. Growth pattern: organised, even, spreading outwards

Mycelium grows in a controlled, circular pattern from the inoculation point.
Common shapes include:

Circular “fluffy” patch

Rhizomorphic strands (rope-like lines)

Dense, cottony centre with feathering edges

✔️ 3. Texture: soft, fluffy, or ropey

Depending on the species:

Oyster → very fast, wispy, cloudy edges

Reishi → slow, dense, almost creamy

Lion’s Mane → fluffy, cloud-like clusters

✔️ 4. Smell (grain/substrate only)

Clean mycelium smells:

mushroomy

fresh

earthy

Never sour, chemical, or funky.

❌ What Contamination Looks Like (With Simple Identifiers)

Contamination can be extremely obvious… or very subtle. Here’s how to recognise each type quickly.

1. Green Mould (Trichoderma)

Colour: bright green or dull green
Texture: powdery
Speed: fast — often exploding overnight

Giveaway sign:
If it starts white but quickly turns green, it’s mould.

2. Bacterial Contamination (“Wet Spot”)

Colour: yellow patches, greasy, shiny
Texture: slimy, wet, sometimes jelly-like
Smell: sour or sweet

On agar:

colonies look blurry, wet, or milky

often causes the mycelium to grow lumpy or uneven

3. Black Mould

Colour: black, grey-black, or charcoal
Texture: dusty or soot-like
Giveaway: spreads in sharp, dark dots

4. Yeast Contamination

Often looks like:

tiny white dots

creamy “splodge” colonies

milky blobs

Grows differently from mycelium because it doesn’t branch or spread in organised lines.

5. Cobweb Mould

Easy to confuse with mycelium.
Colour: very light grey (never pure white)
Texture: wispy, grows in seconds
Test: touch it with a sterile swab — it collapses instantly.

How to Tell the Difference (Simple Rules That Never Fail)

These 5 rules will stop you doubting yourself.

Rule 1 — Mycelium is always white. Anything not white = contamination.

Even slight colour hints (cream, beige, green-grey) are bad signs.

Rule 2 — Mycelium grows with purpose; mould grows messy.

Clean mycelium radiates outwards from the inoculation point in a circle.
Contam grows in random splodges.

Rule 3 — Bacterial contamination looks shiny; mycelium looks matte.

If you see:

wet patches

greasy shine

pools of liquid
It’s bacteria.

Rule 4 — If it spreads extremely fast and looks thin → cobweb.

Mycelium does NOT grow across an agar plate in 24 hours. Cobweb does.

Rule 5 — Different species behave differently — know what "normal" looks like.

A quick cheat sheet:

Oyster

fastest grower

can look “wispy-cloudy” at first

edges grow crazy fast (normal)

Lion’s Mane

slowish

starts as little fluffy cotton balls

does NOT form ropes early on

Reishi

slowest of the three

dense, creamy, almost rubbery texture

red/orange metabolites are normal

Examples of Normal vs Contamination 

Blue Oyster LC

You saw fluffy chunks — perfect. Oyster LC naturally forms floating clouds.

Lion’s Mane LC

Should look like soft white pom-poms. If it forms ropey strands early, it may not be Lion’s Mane.

Reishi LC

Dense white clumps = excellent.
If metabolites form orange “tea” in the liquid, that’s normal.

On agar

Clean = solid white, organised

Contam = any colour, slime, weird shapes

How to Test Cleanliness the Right Way

Make 3–4 transfer spots on agar

Incubate 3–5 days

Check for:

even circular growth

no colours

no shiny/wet sections

Wait an extra 48 hours before declaring it clean

If it stays white → clean.
If anything appears → toss.

⭐ FAQ Section 

Is yellow liquid contamination?

Not always. Mycelium releases metabolites (“mycelium piss”) when stressed or fighting bacteria.
If the colony looks white and clean, it’s fine.

Can mycelium be slightly grey?

No — that’s usually cobweb mould.

Why did one drop on agar contaminate but others were clean?

This happens often.
It usually means the contamination was from the environment, not the syringe.

Can I still use my LC if there’s a small contamination spot?

No — LC spreads contamination everywhere.
If contaminated, discard.

Is it normal for mycelium to stop growing on agar?

Yes — when the plate dries, runs out of nutrients, or the colony matures.

Product Comparison Guide

Product

What You Get

Spore Prints

Clean dried print for microscopy

Spore Syringes

10ml sterile spore suspension

Liquid Culture

Live gourmet culture for legal species

Grain Bags

Sterilised grain with injection port

CVG Substrate

Sterilised coir/vermiculite blend

AIO Bags

Grain + CVG in one sterilised bag